1. Technical Field
The present invention relates to potassium niobate deposited bodies, methods for manufacturing the same, piezoelectric thin film resonators, frequency filters, frequency oscillators, electronic circuits, and electronic apparatuses, which are used in, for example, telecommunications equipment.
2. Related Art
Accompanying the considerable increase in transmission rate in the telecommunications field such as cellular phones and wireless LANs, the transmission frequency is advancing toward higher frequencies in several GHz band and several tens GHz band regions. In the field of technology where such higher frequency rates are expected, piezoelectric thin film resonators (i.e., film bulk acoustic resonators: FBARs) are attracting more attention than surface acoustic wave elements that have been used as frequency filters in the past. Because the development of piezoelectric thin film resonators is also directed toward achieving further miniaturization and higher efficiency, like the direction of development of surface acoustic wave elements, a larger electromechanical coupling coefficient is needed. When a piezoelectric thin film resonator is used as a high frequency filter, in particular, when an ultra wide band is needed as in the case of a UWB (ultra wide band) system, a higher electromechanical coupling coefficient is needed in order to obtain a passband region with a low loss and a wide bandwidth.
Recently, it was found that potassium niobate (KNbO3) (a=0.5695 nm, b=0.5721 nm, and c=0.3973 nm; hereafter this index expression is followed as orthorhombic crystal) single crystal exhibited a large value of electromechanical coupling coefficient. When a, b and c axial directions are assumed to be 1, 3 and 2 directions, respectively, an electromechanical coupling coefficient in a shear distortion mode around the a-axis when an electric filed is impressed in the c-axis direction (i.e., k24) attains a very large value of 46%. Accordingly, it is expected that a piezoelectric thin film resonator having an excellent electromechanical coupling coefficient may be manufactured using this potassium niobate as a thin film. However, there is no technology known to date to form a potassium niobate single phase thin film on a substrate of a large surface area.
It is an object of the present invention to provide a potassium niobate deposited body wherein a polycrystal or single crystal potassium niobate thin layer is formed on a substrate, and a method for manufacturing the same.
It is another object of the present invention to provide a piezoelectric thin film resonator that can be accommodated for higher frequency applications and has a high electromechanical coupling coefficient, with which the effect of miniaturization and power saving can be expected.
It is still another object of the present invention to provide a frequency filter, a frequency oscillator, an electronic circuit, and an electronic apparatus, which include the piezoelectric thin film resonator described above.